Mixed metal oxide catalytic process for the preparation of triethylenediamines

ABSTRACT

A process for preparing bridged nitrogen-containing compounds which comprises contacting a cyclic nitrogen-containing compound reactant with a mixed metal oxide catalyst under conditions effective to produce the bridged nitrogen-containing compound.

RELATED APPLICATIONS

The following are related, commonly assigned applications, filed on an even date herewith:

U.S. patent application Ser. No. 07/585,560; U.S. patent application Ser. No. 07/585,458, now U.S. Pat. No. 5,112,548, and U.S. patent application Ser. No. 07/585,565 all of which are incorporated herein by reference.

BRIEF SUMMARY OF THE INVENTION

1. Technical Field

This invention relates to a process for preparing bridged nitrogen-containing compounds which comprises contacting a cyclic nitrogen-containing compound reactant with a mixed metal oxide catalyst under conditions effective to produce the bridged nitrogen-containing compound.

2. Background of the Invention

Triethylenediamine, also referred to as 1,4-diazabicyclo[2.2.2]octane or DABCO, is an item of commerce which is used as a catalyst for -OH+ OCN- reactions to form the urethane linkage in polyurethanes.

Various processes for the production of triethylenediamine are known. For example, triethylenediamine may be produced by the method disclosed in WO 87/03592, published Jun. 18, 1987. As disclosed therein, triethylenediamine may be produced by bringing an amine compound having a specific amino group into contact with a crystalline metal silicate catalyst wherein the molar ratio of silicon dioxide (SiO₂) to an oxide of a trivalent metal (M₂ O₃ :M being a trivalent metal) is 12 or more.

European Patent Application No. 0158319, published Oct. 16, 1985, discloses a method for preparing 1,4-diazabicyclo[2.2.2]octanes by contacting acyclic or heterocyclic amines with a high-silica zeolite having a silica to alumina ratio of at least 20 to 1.

European Patent Application No. 0263463, published Apr. 13, 1988, discloses a method for preparing 1,4-diazabicyclo[2.2.2]octane and C-substituted 1,4-diazabicyclo[2.2.2]octane by reacting a particular heterocyclic amine in the presence of L-zeolites, phosphates with zeolite structure and zirconium phosphates as catalysts.

Romanian Socialist Republic Specification 85563 discloses a process for the preparation of triethylenediamine characterized by the fact that N,N-dihydroxyethylpiperazine is cyclized in the gaseous phase on a alumina catalyst alkalized with a base chosen from alkali or alkaline earth hydroxides in an amount of from 0.01-10 weight percent based on alumina at a reaction temperature between 200° C. and 550° C., preferably 300° C.-450° C., and an operating pressure between 0.1 and 10 atmospheres.

Copending U.S. patent application Ser. No. 282,371, filed Dec. 13, 1988, relates to processes for the production of amines, more specifically, to processes for preparing triethylenediamine and/or one or more cyclic or acyclic amines by contacting one or more amine starting materials with one or more molecular sieves. By proper choice of catalysts and/or reaction conditions, the processes can be varied to alter their selectivity to a number of differing and useful products, including triethylenediamine and substituted triethylenediamines.

DISCLOSURE OF THE INVENTION

This invention relates to a process for preparing bridged nitrogen-containing compounds which comprises contacting a cyclic nitrogen-containing compound with a mixed metal oxide catalyst under conditions effective to produce the bridged nitrogen-containing compound.

In a preferred embodiment, this invention relates to a process for preparing triethylenediamine which comprises contacting 1,4-bis(2-hydroxyethyl)piperazine in the presence of a magnesium:aluminum mixed metal oxide catalyst under conditions effective to produce triethylenediamine.

The bridged nitrogen-containing compounds produced in accordance with the process of this invention are useful for a wide variety of applications such as polyurethane catalysts, acid scavengers and the like.

For purposes of this invention, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 67th Ed., 1986-87, inside cover. Also, for purposes of this invention, Group IIIB metal oxides embraces the lanthanides and actinides. As used herein, the term "oxide" embraces oxides, hydroxides and/or mixtures thereof.

DETAILED DESCRIPTION

As indicated above, this invention relates to a process for preparing bridged nitrogen-containing compounds which comprises contacting a cyclic nitrogen-containing compound with a mixed metal oxide catalyst under conditions effective to produce the bridged nitrogen-containing compound.

As also indicated above, in a preferred embodiment, this invention relates to a process for preparing triethylenediamine which comprises contacting 1,4-bis(2-hydroxyethyl)piperazine with a mixed metal oxide catalyst, e.g., a magnesium:aluminum mixed metal oxide catalyst, under conditions effective to produce triethylenediamine.

Suitable cyclic nitrogen-containing compound starting materials which can be employed in the process of this invention include any permissible substituted and unsubstituted cyclic nitrogen-containing compound(s) such as piperazine, substituted piperazine, pyrazine, substituted pyrazine and the like. Illustrative cyclic nitrogen-containing compound starting materials include, for example, 1,4-bis(2-hydroxyethyl)piperazine, 1-(2-hydroxyethyl)piperazine, 1,4-bis(2-aminoethyl)piperazine, 1-(2-aminoethyl)piperazine and the like. Illustrative preferred cyclic nitrogen-containing compound starting materials useful in this invention include, for example, 1,4-bis(2-hydroxyethyl)piperazine, 1-(2-hydroxyethyl)piperazine, 1,4-bis(2-aminoethyl)piperazine and 1-(2-aminoethyl)piperazine.

Illustrative of suitable pyrazines which can be employed in the step (1) transesterification reaction include those permissible hydropyrazines, including any permissible derivatives of described hydropyrazines, which are described in Barlin, G. B., Heterocyclic Compounds--The Pyrazines, Vol. 41, 1982, pp. 344-381, the disclosure of which is incorporated herein by reference.

Suitable catalysts which can be employed in the process of this invention include two or more metal oxides. A magnesium:aluminum mixed metal oxide is a preferred mixed metal oxide catalyst as more fully described below. Both homogeneous and heterogeneous catalysts can be employed in the process. The amount of catalyst used in the process is not narrowly critical and is dependent on whether the process is conducted batchwise or continuously. If batchwise, the catalyst employed can range from about 0.01 weight percent or less to about 10 weight percent or greater of the total weight of the starting materials. If continuously, generally a fixed bed is employed.

Suitable catalysts for use in the process of this invention comprise two or more metal oxides. Illustrative of such mixed metal oxides include, for example, two or more of the following: Group IA metal oxides, Group IIA metal oxides, Group IIIB metal oxides (including lanthanides and actinides), Group IVB metal oxides, Group VB metal oxides, Group VIB metal oxides, Group VIIB metal oxides, Group VIII metal oxides, Group IB metal oxides, Group IIB metal oxides, Group IIIA metal oxides, Group IVA metal oxides, Group VA metal oxides or Group VIA metal oxides. Preferred mixed metal oxides are amphoteric or basic. Preferred mixed metal oxides which may be utilized as catalysts include, for example, two or more oxides of magnesium, aluminum, calcium, strontium, gallium, beryllium, barium, scandium, yttrium, lanthanum, cerium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, lutetium, ytterbium, niobium, tantalum, chromium, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, iron, cobalt, nickel, zinc, silver, cadmium, boron, indium, silicon, germanium, tin, lead, arsenic, antimony and bismuth.

Group IIA metal oxides such as magnesium oxide and calcium oxide and Group IIIA metal oxides such as aluminum oxide and gallium oxide are preferred mixed metal oxides for use in this invention. For mixed metal oxides in which at least one of the metals is magnesium, suitable metals in association with magnesium may include, for example, one or more of the following: Group IIIA metals such as boron, aluminum, gallium and indium, Group IIIB metals such as scandium, yttrium and lanthanum including the lanthanides, Group VB metals such as niobium and tantalum, Group VIB metals such as chromium, molybdenum and tungsten, Group VIII metals such as iron, cobalt and nickel, Group IIB metals such as zinc and cadmium, Group IVA metals such as silicon, germanium, tin and lead, Group VA metals such as arsenic, antimony and bismuth, and Group IVB metals such as zirconium and hafnium. For mixed metal oxides in which at least one of the metals is calcium, suitable metals in association with calcium may include, for example, one or more of the following: Group IIIA metals such as boron, aluminum, gallium and indium, Group IVA metals such as silicon, germanium, tin and lead, Group VB metals such as niobium and tantalum, and Group VIB metals such as chromium, molybdenum and tungsten.

Illustrative of mixed metal oxides which may be used as catalysts include, for example, MgO-Al₂ O₃, MgO-SiO₂, MgO-CdO, MgO-Bi₂ O₃, MgO-Sb₂ O₅, MgO-SnO₂, MgO-ZrO₂, MgO-BeO, MgO-TiO₂, MgO-CaO, MgO-SrO, MgO-ZnO, MgO-Ga₂ O₃, MgO-Y₂ O₃, MgO-La₂ O₃, MgO-MoO₃, MgO-Mn₂ O₃, MgO-Fe₂ O₃, MgO-Co₃ O₄, MgO-WO₃, MgO-V₂ O₅, MgO-Cr₂ O₃, MgO-ThO₂, MgO-Na₂ O, MgO-BaO, MgO-CaO, MgO-HfO₂, MgO-Li₂ O, MgO-Nb₂ O₅, MgO-Ta₂ O₅, MgO-Gd₂ O₃, MgO-Lu₂ O₃, MgO-Yb₂ O₃, MgO-CeO₂, MgO-Sc₂ O₃, MgO-PbO, MgO-NiO, MgO-CuO, MgO-CoO, MgO-B₂ O₃, CaO-SiO₂, CaO-Al₂ O₃, CaO-SnO, CaO-PbO, CaO-Nb₂ O₅, CaO-Ta₂ O₅, CaO-Cr₂ O₃, CaO-MoO₃, CaO-WO₃, CaO-TiO₂, CaO-HfO₂, MgO-SiO₂ -Al₂ O₃, MgO-SiO₂ -ZnO, MgO-SiO₂ -ZrO.sub. 2, MgO-SiO₂ -CuO, MgO-SiO₂ -CaO, MgO-SiO₂ -Fe₂ O₃, MgO-SiO₂ -B₂ O₃, MgO-SiO₂ -WO₃, MgO-SiO₂ -Na₂ O, MgO-SiO₂ -Ga₂ O₃, MgO-SiO₂ -La₂ O₃, MgO-SiO₂ -Nb₂ O₅, MgO-SiO₂ -Mn₂ O₃, MgO-SiO₂ -Co₃ O₄, MgO-SiO₂ -NiO, MgO-SiO₂ -PbO, MgO-SiO₂ -Bi₂ O₃, MgO-Al₂ O₃ -ZnO, MgO-Al₂ O₃ -ZrO₂, MgO-Al₂ O₃ -Fe₂ O₃, MgO-Al₂ O₃ -WO₃, MgO-Al₂ O₃ -La₂ O₃, MgO-Al₂ O₃ -Co₃ O₄, CaO-SiO₂ -Al₂ O₃, CaO-SiO₂ -SnO, CaO-SiO₂ -Nb₂ O₅, CaO-SiO₂ -WO₃, CaO-SiO₂ -TiO₂, CaO-SiO₂ -MoO₃, CaO-SiO₂ -HfO₂, CaO-SiO₂ -Ta₂ O₅, CaO-Al₂ O₃ -SiO₂, CaO-Al₂ O₃ -PbO, CaO-Al₂ O₃ -Nb₂ O₅, CaO-Al₂ O₃ -WO₃, CaO-Al₂ O₃ -TiO₂, CaO-Al₂ O₃ -MoO₃, CaO-HfO₂ -Al₂ O₃, CaO-HfO₂ -TiO₂, and the like. Other suitable mixed metal oxides embraced within the scope of this invention are disclosed by Tanabe et al., Bulletin of the Chemical Society of Japan, Vol. 47(5), pp. 1064-1066 (1974).

The mixed metal oxides described herein which can be used as catalysts may contribute to product selectivity and/or catalytic activity of the reaction and/or stability of the catalyst. As discussed hereinafter, the catalyst employed in this invention may also contain support(s), binding agent(s) or other additives to stabilize or otherwise help in the manufacture of the catalyst.

The catalysts which comprise two or more metal oxides may be prepared in a wide variety of ways. For example, the two or more metal oxides can be provided from metal salts which can either be heated or precipitated to form the mixed metal oxides. Also, two or more metal oxides may be provided as a partial condensate on a support, such as a silica or alpha, beta or gamma alumina, silicon carbide, and the like, and then condensed by heating to effect polymerization to the desired oxide form. The two or more metal oxides may be condensed from hydrolyzable monomers to the desired oxides, indeed, to form oxide powders which can thereafter be compressed in the presence of a condensation catalyst to form pellets and larger structures of the mixed metal oxide catalyst. A blend of the powders and condensation catalyst can be made into a shapeable paste which can be extruded and cut into pellets according to conventional procedures. The extrudate may thereafter be fired to cure the condensation catalyst and fix the structure. The cut extrudate may be blended with a support material such as those characterized above, and the blend fired to fuse the mixed metal oxide catalyst to the support.

In an embodiment of this invention, a magnesium salt, e.g., magnesium nitrate, and an aluminum salt, e.g., aluminum nitrate, are precipitated using ammonium hydroxide. The material is then washed with deionized water and calcined at a temperature of from about 350° C. to about 450° C. to afford the desired magnesium:aluminum mixed metal oxide catalyst.

In another embodiment, a magnesium oxide, e.g., magnesium carbonate hydroxide pentahydrate, and an aluminum oxide, e.g., aluminum hydroxide hydrate, are added to deionized water and thoroughly mixed to form a paste. The paste is then calcined at a temperature of from about 350° C. to about 450° C. to afford the desired magnesium:aluminum mixed metal oxide catalyst.

A preferred catalyst structure comprises a Group IIA and IIIA mixed metal oxide having a surface area of at least about 100 m² /gm which may or may not be bonded to a support material. The catalysts on a support preferably have a surface area greater than about 20 m² /gm to as high as about 260 m² /gm, or greater depending upon which metal oxides are employed. In the case of magnesium:aluminum oxides, the surface area can be greater than about 50 m² /gm to as high as about 260 m² /gm, more preferably, greater than about 100 m² /gm to as high as about 260 m² /gm, determined according to the single point N₂ method.

The term "support," as used herein and in the claims, means a solid structure which does not adversely affect the catalytic properties of the catalyst and is at least as stable as the catalyst to the reaction medium. The support can function as a catalyst independent of the mixed metal oxide catalyst used herein, although it may have lower catalytic activity to the reaction. The support may act in concert with the catalyst to moderate the reaction. Some supports may contribute to the selectivity of the reaction. The catalyst structure can comprise from about 2 to about 60 percent by weight or greater of the support, more preferably from about 10 to about 50 percent by weight of the support, the remainder being the weight of the mixed metal oxides. Included in the weight of the support is the weight of any binding agent such as phosphates, sulfates, silicates, fluorides, and the like, and any other additive provided to stabilize or otherwise help in the manufacture of the catalyst. The support may be particles as large or larger than the catalyst component and "glued" to the catalyst by virtue of a binding medium.

The support may constitute a separate phase in the process of extruding the catalytic structure. In this embodiment, the support forming material, preferably as a paste is blended with a paste of the catalyst or a partial condensate thereof. The paste may comprise the oxide forms of the support and the catalyst, each blended with water, and/or binding agents. The extrudate of the blend is passed through a multiorificed die and chopped into pellets of the desired sizes. The particles may be doughnut shaped, spherical, and the like. Then the particles are calcined to dry them and complete any condensation reaction in the support and/or the mixed metal oxide catalyst.

A preferred group of mixed metal oxide catalysts for use in this invention include materials having the formula:

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (OH).sub.2x+3y-nz A.sub.z.sup.n.sub.-.aH.sub.2 O                            (I)

wherein M is at least one divalent metal cation; Q is at least one trivalent metal cation; and A is at least one anion providing a valence (n⁻), wherein n is at least 1, e.g., between 1 and 4 and most often between 1 and 3, and wherein a is a positive number, M, Q, and A are provided in a proportion such that x/y is a number equal to or greater than 1, z has a value greater than zero and 2x+3y-nz is a positive number. M, Q and A may be selected to provide a layered structure. Preferably, x/y is in the range of 1 to 12, more preferably x/y is in the range of 1 to 6 and most preferably is in the range of 1 to 4. Preferably, z has a value such that x/z is between n and 12n, more preferably between n and 6n and most preferably between n and 4n.

Suitable divalent metal cations, M, broadly include elements selected from the Transition elements and Groups IIA and IVA of the periodic Table as well as certain Group IIIB elements. As specific examples can be mentioned magnesium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, palladium, platinum, copper, zinc, cadmium, mercury, tin and lead. Divalent metal cations which are particularly suitable are magnesium, nickel, cobalt, zinc, calcium, strontium and copper. Suitable trivalent metal cations, Q, broadly include elements selected from the Transition elements and Groups IIIA and VA of the periodic Table as well as certain Group IIIB elements. As specific examples can be mentioned aluminum, antimony, titanium, scandium, bismuth, vanadium, yttrium, chromium, iron, manganese, cobalt, ruthenium, nickel, gold, gallium, thallium, and cerium. Trivalent metal cations which are particularly suitable can be selected from aluminum, boron, gallium and lanthanum.

The composition of formula (I) also can include a wide range of anions, A. Any anion or combination of anions which can balance the charge of the cations can be used. Suitable anions include inter alia, halides (such as chloride, fluoride, bromide, and iodide), nitrite, nitrate, sulfite, sulfate, sulfonate, carbonate, chromate, cyanate, phosphite, phosphate, molybdocyanate, bicarbonate, hydroxide, arsenate, chlorate, ferrocyanide, borate, cyanide, cyanaurate, cyanaurite, ferricyanide, selenate, tellurate, bisulfate, as well as organic anions such as oxalate, acetate, hexanoate, sebacate, formate, benzoate, malonate, lactate, oleate, salicylate, stearate, citrate, tartrate, maleate, and the like. The class of metalate anions described in U.S. Pat. No. 4,667,045, including metavanadate, orthovanadate, molybdate, tungstate, hydrogen pyrovanadate and pyrovanadate, also are suitable as anion A. Anions suitable for use in combination with the metal cations previously identified as being particularly suitable are carbonate, halide, phosphate, chromate, sulfate, hydroxide, oxalate, acetate, nitrate, hexanoate, sebacate, vanadate, molybdate, tungstate and ferrocyanate.

The foregoing lists of suitable divalent and trivalent cations and suitable anions are meant to be illustrative and not exclusive. Those skilled in the art will recognize that other cations and anions can be used provided that the specific type of cations and their relative amounts (x/y ratio) and the specific type of anions and their relative amount result in a mixed metal oxide composition.

Included in the materials identified above are those based on exchangeable anionic clay minerals. For example, compositions of formula (I) wherein M is magnesium and Q is aluminum are related to hydrotalcites, while compositions in which M is nickel and A is aluminum are related to takovites. In fact, mixed metal oxides prepared using magnesium, nickel or cobalt as the divalent cation and aluminum as the trivalent cation exhibit the typical X-ray diffraction pattern of a hydrotalcite.

In another preferred aspect, the process of this invention can utilize mixed metal oxide catalyst compositions prepared by calcining at an elevated temperature compositions according to formula (I). Suitable calcined compositions have the general formula:

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (O).sub.2x+3y-nz)/2 D.sub.z.sup.n-(II)

wherein M, Q, x, y, z and n have the same meanings defined above in connection with formula (I), and D is at least one nonvolatile anion. Nonvolatile anions may include, inter alia, halides, nitrates, phosphites, phosphate, vanadate, molybdate, tungstate, sulfite, sulfate, chromate, arsenate, borate, chlorate and the like. This list is illustrative and not exclusive.

Heat treating the formula (I) compositions to prepare the calcined mixed metal oxide compositions of formula (II) can be done, for example, at a temperature in the range of 200° C. to 800° C. for a period of time of about 12 to 24 hours under an inert atmosphere such as nitrogen or in appropriate cases under an oxidizing atmosphere such as air.

Calcination of the mixed metal oxide composition dehydrates the composition and converts at least partially the metal hydroxides to metal oxides. Any nonvolatile anions may be present in the calcined material.

Provided the calcination temperature is not excessive, the mixed metal oxide can be rehydrated to the mixed metal hydroxide with water. Generally, the mixed metal oxide can be restored readily if the calcination temperature does not exceed about 600° C. Mixed metal oxides which are calcined under more severe conditions are not easily rehydrated and lower surface area materials are obtained.

Certain compositions falling within formula (I), such as hydrotalcite, which comprises a magnesium-aluminum hydroxide carbonate, and takovite, which comprises a nickel-aluminum hydroxide carbonate, are naturally occurring compositions. However, such compounds, as well as their related compositions, also can be prepared synthetically from inexpensive starting materials using well-known coprecipitation techniques. Procedures for direct synthesis of such materials are described in Itaya et al., Inorg. Chem. (1987) 26:624-626; Taylor, R. M., Clay Minerals (1984) 19:591-603; Reichle, U.S. Pat. No. 4,476,324; Bish, D. L., Bull. Mineral (1980), 103:170-175 and Miyata et al., Clays and Clay Minerals (1977), 25:14-18. Using direct synthesis one has the ability to vary within wide limits the M⁺² /Q⁺³ atomic ratio as well as the anion.

For example, a composition of formula (I) where M⁺² is nickel or magnesium, Q⁺³ is aluminum and A^(n-) is carbonate can be prepared by adding, as aqueous solutions, (a) a mixture of nitrates, sulfates or chlorides of nickel or magnesium and aluminum in a desired atomic ratio of nickel or magnesium to aluminum, e.g., 6 atoms of nickel as nickel chloride to 2 atoms of aluminum as aluminum chloride, to (b) an aqueous solution of a stoichiometric amount of sodium hydroxide and a water soluble salt of the desired anion, e.g., sodium carbonate. The two solutions are mixed at a temperature of about 25° C. to 35° C. with vigorous stirring over a several-hour period to produce a slurry. The slurry then is heated for about 18 hours at a temperature within the range of about 50° C. to 200° C. (preferably between about 60° C. to 75° C.) in order to control crystallization and the ultimate particle size of the resulting crystals. After filtering, and thorough washing and drying, the solids are recovered, typically as a powder.

As noted above, this procedure can be adapted to a wide variety of cations, cation atomic ratios and anion substitutions. For example, water soluble salts of divalent magnesium, cobalt, zinc, copper, iron and calcium can be substituted for the nickel chloride illustrated above, while water soluble salts of trivalent gallium and lanthanum can replace the aluminum chloride. A wide variety of other combinations also will be apparent to those skilled in the art. Generally, the rate of metal ion addition to the aqueous caustic/anion solution is not critical and can be varied widely. For example, a preferred preparation method is described in Schaper, H. et al., Applied Catalysis, 54, 1989, 79-90, the disclosure of which is incorporated herein by reference. The reaction temperature also is not critical, although the temperature during the reaction preferably is kept below about 100° C. An important feature of the procedure is the use of efficient agitation during the mixing procedure to avoid the formation of undesired by-products.

Loading of an anion A or D into the mixed metal oxide compositions is influenced by a variety of factors including (i) the amount of anion used in the preparation relative to the metal cations, (ii) the atomic ratio of the metal cations (x/y) in the preparation procedure, (iii) the size of the cations and anions and (iv) the preparation procedure. As used herein, "loading" is defined as the amount of available valences provided by a desired anion A or D expressed as a percentage of the total available valences for anion A or D. For example, carbonate loading in a hydrotalcite-type catalyst can be maximized by (i) using an excess (e.g., a greater than 3:1 molar ratio) of sodium carbonate to aluminum chloride during catalyst preparation and (2) adjusting the atomic ratio of magnesium to aluminum cations to about 2:1.

Mixed metal oxide compositions suitable as catalysts also can be prepared from the native or synthetic hydrotalcite-type compositions by ion exchange. For example, hydrotalcite can be treated at ambient conditions with 0.01 N phosphoric acid for about 18 hours to replace the carbonate anion with phosphate anion. A halide analog of hydrotalcite prepared directly or by anion-exchange could be contacted with molybdic acid or a water soluble salt thereof, or with a water soluble salt of tungstic acid or vanadic acid in order to substitute the transition metal anion for the halide anion in the catalyst structure thereby to produce a mixed metal oxide composition of formula (I). Other ion exchanges will be apparent to those skilled in the art.

Calcined mixed metal oxide compositions may exhibit a higher level of selectivity/activity than uncalcined compositions. If a calcined mixed metal oxide catalyst composition experiences any decline in selectivity, it can be regenerated by a heat treatment in the presence of air to restore at least a portion of its initial level of selectivity/activity enhancement and reused. Conditions discussed above for calcining the hydrated mixed metal oxide compositions are suitable for regenerating compositions which have experienced a decline in activity.

Catalysts having the formulas (I) and (II) above wherein M is at least one of magnesium and calcium, Q is aluminum or gallium, A is at least one of carbonate, bicarbonate, phosphate, sulfate and nitrate, x/y is between 1 and 20, z has a value which satisfies the relationship: x/z is between n and 12n, and a is a positive number, are generally preferred for vapor phase decarboxylation due to their combination of activity (conversion of precursor) and selectivity. A preferred process involves a vapor phase process using mixed metal oxide catalyst wherein M²⁺ is magnesium, Q³⁺ is aluminum, A^(n-) is carbonate, x/y is about 1, and z is about 1.

A group of preferred mixed metal oxide catalyst compositions which can be employed in the process of this invention is disclosed in copending U.S. patent application Ser. No. 125,134, filed Nov. 25, 1987, now abandoned in favor of continuation application Ser. No. 527,375, filed May 23, 1990), the disclosure of which is incorporated herein by reference.

The process of this invention may be effected in the liquid or vapor or supercritical liquid states or mixtures thereof. In this context, the vapor phase reaction is intended to refer to the general vapor state of the starting materials. Though the process conditions may range from subatmospheric or atmospheric to superatmospheric conditions, it is desirable to run the process from about 1 mm Hg to about 5,000 :mm Hg, preferably from about 100 mm Hg to about 2,500 mm Hg.

The temperature of the process may be as low as about 150° C. to about 500° C. Preferably, the reaction temperature ranges from about 175° C. to about 375° C., and most preferably from about 225° C. to about 350° C.

The process can be conducted in the presence of an inert diluent which can be either a liquid or gas. When a liquid diluent is employed, it should preferably be a good solvent for the starting materials, inert under the reaction conditions, and of such a nature that separation from the bridged nitrogen-containing compound product will not be difficult. For instance, the boiling points of the diluent and the bridged nitrogen-containing compound product should differ by an adequate amount and there should be no tendency of the diluent to form an azeotrope with the desired bridged nitrogen-containing compound product.

Examples of useful liquid diluents that meet the foregoing qualifications include water, benzene, toluene, xylene, ethylbenzene, anisole, heptane, octane, nonane, decane, dibutyl ether, and the like. Hydrocarbons are preferred.

Illustrative gaseous diluents include for example, nitrogen, methane, hydrogen, carbon monoxide or carbon dioxide. The gaseous diluent should of course be chosen so that it does not prevent the preparation of the desired products.

While the use of such diluents may be beneficial, the process of this invention can be operated using pure starting material(s) as a liquid or gaseous feed. The degree of dilution of the starting materials with various diluents may vary considerably depending upon any process constraints restricting the use of the diluent. For example, in commercial production, the use of very large quantities of some gaseous diluents may be disadvantageous due to the cost of pumping large volumes of the gaseous diluent and increased difficulty in isolating the product, which increase the energy costs of the process. With liquid diluents, the use of very large quantities may be disadvantageous due to the energy cost associated with large recovery and recycle. If the process of this invention is to be carried out using a gaseous diluent, in general it is recommended that the starting material(s) constitute from about 1 to about 95, and preferably about 5 to about 50, mole percent of the starting material/carrier feed. Increasing the dilution of the starting material with a gaseous diluent such as hydrogen may tend to increase the selectivity of the reaction to the particular products desired. The amount of liquid diluent can vary widely, for instance, from no diluent to about 90 weight percent or greater of the total weight of the starting materials.

The process of this invention is useful for preparing substituted and unsubstituted bridged nitrogen-containing compounds such as triethylenediamine, substituted triethylenediamines and the like. Illustrative bridged nitrogen-containing compounds prepared by the processes of this invention include, for example, triethylenediamine, 2-methyl-triethylenediamine and the like.

Illustrative of suitable bridged nitrogen-containing compounds which can be prepared by the process of this invention include those permissible bridged nitrogen-containing compounds, including any permissible derivatives of described bridged nitrogen-containing compounds, which are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, 1984, the pertinent portions of which are incorporated herein by reference.

The bridged nitrogen-containing compound products produced by the process of this invention can be separated by distillation. For example, a crude reaction product can be subjected to a distillation-separation at atmospheric or reduced pressure through a packed distillation column. Reactive distillation may be useful in conducting the process of this invention.

The process of this invention may be carried out using, for example, a fixed bed reactor, a fluid bed reactor, or a slurry reactor. The optimum size and shape of the catalyst will depend on the type of reactor used. In general, for fluid bed reactors, a small, spherical catalyst particle is preferred for easy fluidization. With fixed bed reactors, larger catalyst particles are preferred so the back pressure within the reactor is kept reasonably low.

The process of this invention can be conducted in a batch or continuous fashion, with recycle of unconsumed starting materials if required. The reaction can be conducted in a single reaction zone or in a plurality of reaction zones, in series or in parallel or it may be conducted batchwise or continuously in an elongated tubular zone or series of such zones. The materials of construction employed should be inert to the starting materials during the reaction and the fabrication of the equipment should be able to withstand the reaction temperatures and pressures. Means to introduce and/or adjust the quantity of starting materials or ingredients introduced batchwise or continuously into the reaction zone during the course of the reaction can be conveniently utilized in the processes especially to maintain the desired molar ratio of the starting materials. The reaction steps may be effected by the incremental addition of one of the starting materials to another. Also, the reaction steps can be combined by the joint addition of the starting material(s) to the catalyst. When complete conversion is not desired or not obtainable, the starting materials can be separated for the bridged nitrogen-containing compound product, for example by distillation, and the starting materials then recycled back into the reaction zone.

The process is conducted for a period of time sufficient to produce the bridged nitrogen-containing compound products. The exact reaction time employed is dependent, in part, upon factors such as temperature, nature and proportion of starting material(s), and the like. The reaction time will normally be within the range of from about one-half to about 100 hours or more, and preferably from less than about one to about ten hours.

The process may be conducted in either glass lined, stainless steel or similar type reaction equipment. The reaction zone may be fitted with one or more internal and/or external heat exchanger(s) in order to control undue temperature fluctuations, or to prevent any possible "runaway" reaction temperatures.

Illustrative of suitable reactants in effecting the process of this invention include by way of example:

    ______________________________________                                         PIP          piperazine                                                        HEP          1-(2-hydroxyethyl)piperazine                                      DHEP         1,4-bis(2-hydroxyethyl)piperazine                                 HPP          1-(2-hydroxypropyl)piperazine                                     ______________________________________                                    

Illustrative of suitable products prepared by the process of this invention include by way of example:

    ______________________________________                                         TEDA           triethylenediamine                                              MTEDA          2-methyl-triethylenediamine                                     ______________________________________                                    

Illustrative of permissible reactions encompassed within the scope of this invention include, for example, the following reactant/product combinations:

    ______________________________________                                         REACTANTS      PRODUCT(s)                                                      ______________________________________                                         DHEP           TEDA                                                            HEP            TEDA                                                            HPP            MTEDA                                                           ______________________________________                                    

As used herein, the phrase "residue of an organic compound" is contemplated to include all permissible residues of organic compounds. In a broad aspect, the permissible residues include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic residues of organic compounds. Illustrative organic compound residues include, for example, alkyl, aryl, cycloalkyl, heterocycloalkyl, alkyl(oxyalkylene), aryl(oxyalkylene), cycloalkyl(oxyalkylene), heterocycloalkyl(oxyalkylene), hydroxyalkyl, hydroxyalkyl(oxyalkylene), hydroxy(alkyleneoxy) and the like. The permissible residues can be substituted or unsubstituted and the same or different for appropriate organic compounds. This invention is not intended to be limited in any manner by the permissible residues of organic compounds.

As used herein, the term "substituted" is contemplated to include all permissible substituents of organic compounds. In a broad aspect, the permissible substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic substituents of organic compounds. Illustrative substituents include, for example, alkyl, alkyloxy, aryl, aryloxy, hydroxy, hydroxyalkyl, amino, aminoalkyl, halogen and the like in which the number of carbons can range from 1 to about 20 or more, preferably from 1 to about 12. The permissible substituents can be one or more and the same or different for appropriate organic compounds. This invention is not intended to be limited in any manner by the permissible substituents of organic compounds.

Certain of the following examples are provided to further illustrate the process of this invention.

The following apparatus was used for the preparation of bridged nitrogen-containing compounds in the examples. An Applied Test Systems, Inc. Model 3620 Split Test Oven equipped with a preheater (stainless steel 1/8 inch o.d.×2 feet) and 1/2 inch (o.d.) stainless steel reactor tube (8 inch length) was packed with catalyst and heated to the desired reaction temperature using a Honeywell Dial-A-Trol temperature controller. The temperatures at the top of the reactor and the bottom were monitored using a digital temperature readout. The liquid feed was added (downflow) to the reactor via a Fluid Metering Inc. RP-G20 drive pump equipped with an 1/8 inch pump head. The system was maintained under nitrogen, which was introduced after the liquid preheater. The product mixture was collected in a 100 milliliter round bottom flask, vented first to a dry ice/acetone trap and then a Firestone valve. Analysis was performed by capillary gas chromatography (FID) using a DB-1701 column.

EXAMPLE 1 Preparation of Decarboxylation Catalyst

A total of 44.1 grams of magnesium nitrate hexahydrate and 66.0 grams of aluminum nitrate nonahydrate were dissolved in 200 milliliters of distilled water to give a first solution. A total of 4.8 grams of ammonium carbonate was dissolved in 200 milliliters of concentrated ammonium hydroxide (28-29 weight percent) to give a second solution. About 100 milliliters of distilled water was heated in a flask at a temperature of 40° C. and the first and second solutions were combined simultaneously with good agitation using a mechanical stirrer. The rates of addition of the first and second solutions were adjusted to maintain a pH of 9-10. The total addition took 10 minutes and a final pH of 9.5 was obtained. The contents were stirred at a temperature of 40° C. for a period of 40 minutes. The resulting precipitate was filtered and washed (ca. 300 milliliters three to four times) with water at a temperature of 60° C. until the pH of the wash was neutral. The filter cake was dried at a temperature of 80° C. overnight. The weight of the dried filter cake was about 16 grams. The filter cake was then calcined in air at a temperature of 400° C. for a period of 3 hours to afford a magnesium:aluminum mixed metal oxide.

EXAMPLE 2 Preparation of Triethylenediamine

Using the apparatus described hereinabove, a 50 weight percent solution of 1-(2-hydroxyethyl)piperazine in water was passed through a catalyst bed containing 6.0 grams of a magnesium:aluminum mixed metal oxide (1/8 inch tablets, Mg/Al 3:1) at a temperature of 325° C. and a liquid feed rate of 0.25 milliliters per minute. After a period of 40 minutes, the run was stopped and the reactor effluent analyzed. The results are given in Table I below.

                  TABLE I                                                          ______________________________________                                         Product Composition, area %:                                                   ______________________________________                                         Piperazine            17.4                                                     Triethylenediamine    9.5                                                      1-(2-hydroxyethyl)piperazine                                                                         57.6                                                     1,4-bis(2-hydroxyethyl)piperazine                                                                    4.5                                                      Others                11.1                                                     ______________________________________                                    

EXAMPLE 3 Preparation of Triethylenediamine

Using the apparatus described hereinabove, a 30 weight percent solution of 1,4-bis(2-hydroxyethyl)piperazine in water was passed through a catalyst bed containing 6.0 grams of a magnesium:aluminum mixed metal oxide (1/8 inch tablets, Mg/Al 3:1) at a temperature of 325° C. and a liquid feed rate of 0.22 milliliters per minute. After a period of 30 minutes, the run was stopped and the reactor effluent analyzed. The results are given in Table II below.

                  TABLE II                                                         ______________________________________                                         Product Composition, area %:                                                   ______________________________________                                         Piperazine            9.8                                                      Triethylenediamine    48.6                                                     1-(2-hydroxyethyl)piperazine                                                                         15.7                                                     1,4-bis(2-hydroxyethyl)piperazine                                                                    10.1                                                     Others                15.8                                                     ______________________________________                                    

EXAMPLE 4

Using the apparatus described hereinabove, a 30 weight percent solution of 1,4-bis(2-hydroxyethyl)piperazine in water was passed through the reactor tube described above packed with glass pellets at a temperature of 325° C. and a liquid feed rate of 0.25 milliliters per minute. After a period of 0.5 hours, the run was stopped and the reactor effluent analyzed. The results are given in Table III below.

                  TABLE III                                                        ______________________________________                                         Product Composition, area %:                                                   ______________________________________                                         1-(2-hydroxyethyl)piperazine                                                                         4.1                                                      1,4-bis(2-hydroxyethyl)piperazine                                                                    94.4                                                     Others                1.2                                                      ______________________________________                                    

Although the invention has been illustrated by certain of the preceding examples, it is not to be construed as being limited thereby; but rather, the invention encompasses the generic area as hereinbefore disclosed. Various modifications and embodiments can be made without departing from the spirit and scope thereof. 

I claim:
 1. A process for preparing triethylenediamine or 2-methyl-triethylenediamine which comprises contacting a cyclic nitrogen-containing compound selected from the group consisting of 1-(2-hydroxyethyl)piperazine, 1,4-bis(2-hydroxyethyl)piperazine, 1-(2-hydroxypropyl)piperazine, 1-(2-aminoethyl)piperazine and 1,4-bis(2-aminoethyl)piperazine, with a mixed metal oxide catalyst comprising:(a) a material having the formula

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (OH).sub.2x+3y-nz A.sub.z.sup.n-.aH.sub.2 O (I)

wherein M is magnesium; Q is aluminum; and A is at least one anion providing a valence (n⁻), wherein n is 1 to 4 and wherein a is a positive number, M, Q and A are provided in a proportion such that z/y is a number equal to or greater than 1, z has a value greater than zero such that x/z is between n and 12n, and 2x+3y-nz is a positive number, or (b) a material prepared by calcining the material of formula (I) having the formula

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (O).sub.(2x+3y-nz)/2 D.sub.z.sup.n-(II)

wherein M, Q, x, y, z and n have the same meanings defined above in connection with formula (I), and D is at least one nonvolatile anion; under conditions effective to produce triethylenediamine or 2-methyl-triethylenediamine.
 2. The process of claim 1 wherein the mixed metal oxide catalyst is associated with a support material.
 3. The process of claim 2 wherein the support comprises an alumina material or an alumina-silica material.
 4. The process of claim 2 wherein the support comprises a silica material or a silica-alumina material.
 5. The process of claim 2 wherein the support comprises from about 2 to about 50 percent by weight of the mixed metal oxide catalyst.
 6. The process of claim 1 wherein x/y is a number between 1 and 12 and z has a value which satisfies the relationship: x/z is between n and 12n.
 7. The process of claim 1 wherein A is selected from the group consisting of carbonate, halide, phosphite, phosphate, chromate, sulfate, hydroxide, oxalate, acetate, nitrate, hexanoate, sebacate, vanadate, molybdate, tungstate and ferrocyanate.
 8. The process of claim 1 wherein D is selected from the group consisting of halides, phosphite, phosphate, vanadate, molybdate, tungstate, sulfite, sulfate, chromate, arsenate, borate and chlorate.
 9. The process of claim 1 wherein x/y is a number between 1 and 6 and z has a value which satisfies the relationship: x/z is between n and 6n.
 10. The process of claim 1 wherein said material prepared by calcining the material of formula (I) has been heat treated at a temperature in the range of 200° C. to 800° C. for 12 to 24 hours.
 11. The process of claim 1 wherein the temperature is from about 150° C. to about 500° C.
 12. The process of claim 1 wherein the temperature is from about 175° C. to about 375° C.
 13. The process of claim 1 wherein the reaction time is from about 0.5 hours to about 100 hours.
 14. A process for preparing triethylenediamine which comprises contacting 1,4-bis(hydroxyethyl)piperazine with a catalyst consisting essentially of a magnesium:aluminum mixed metal oxide under conditions effective to produce triethylenediamine. 